TiO2 nanostructures, membranes and films, and applications of same

ABSTRACT

The present invention relates to applications of TiO 2 -containing, macro-sized nanostructures in the fields including photocatalysis, information writing-erasing-rewriting, microfiltration, controlled drug release, and tire making. In one aspect, the present invention relates to a method of photocatalytically decomposing organic pollutants. In one embodiment, the method includes the steps of mixing a solution containing organic pollutants and a plurality of TiO 2 -containing, macro-sized nanostructures to form a mixture and exposing the mixture to UV irradiation to decompose the organic pollutants.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit, pursuant to 35 U.S.C. §119(e), ofU.S. provisional patent application Ser. Nos. 60/758,492, filed Jan. 12,2006, entitled “TiO₂ NANOFIBER MEMBRANES, METHODS OF MAKING SAME, ANDAPPLICATIONS OF SAME” by Z. Ryan Tian and Wenjun Dong, and 60/785,649,filed Mar. 23, 2006, entitled “TiO₂NANOFIBERS, MEMBRANES, AND FILMS,METHODS OF MAKING SAME, AND APPLICATIONS OF SAME” by Z. Ryan Tian andWenjun Dong, which are incorporated herein by reference in theirentireties.

This application is related to a co-pending U.S. patent application,entitled “TiO₂ NANOSTRUCTURES, MEMBRANES AND FILMS, AND METHODS OFMAKING SAME” by Z. Ryan Tian, which was filed on the same day that thisapplication was filed, and with the same assignee as that of thisapplication. The disclosure of the above identified co-pendingapplication is incorporated herein by reference in its entirety.

Some references, which may include patents, patent applications andvarious publications, are cited and discussed in the description of thisinvention. The citation and/or discussion of such references is providedmerely to clarify the description of the present invention and is not anadmission that any such reference is “prior art” to the inventiondescribed herein. All references cited and discussed in thisspecification are incorporated herein by reference in their entiretiesand to the same extent as if each reference was individuallyincorporated by reference. In terms of notation, hereinafter, “[n]”represents the nth reference cited in the reference list. For example,[10] represents the 10th reference cited in the reference list, namely,Tian, Z. R., Voigt, J, A., Liu, J., Mckenzie, B., Xu, H., J. Am. Chem.Soc., 2003, 125, 12384.

FIELD OF THE INVENTION

The present invention relates generally to nanostructures and inparticular to TiO₂-containing, macro-sized nanostructures, methods ofmaking same, and applications of same.

BACKGROUND OF THE INVENTION

Great efforts are currently devoted to the studies on one-dimensional(1D) nanostructures due to a wealth of unique physical and chemicalproperties associated with the 1D structural confinement in nanoscale[1]. Due to their high thermal stability and chemical inertness,inorganic nanofibers including nanowires and nanotubes can be assembledinto a free standing membrane (FSM) for important applications at hightemperatures and in harsh environments [2]. To make the FSM robust, theinorganic nanofibers should be ultra-long and “woven” properly. Suchinorganic FSMs could then possess unique porosity, permeability, thermalstability, chemical inertness, robustness, and catalytic properties, allof which would largely differentiate the nanofiber FSMs from themonodispersed nanofibers and the bulk phases of the same/similarchemical formula.

The fabrication of inorganic nanostructured FSM was demonstrated in 1996on the growth of an oriented mesoporous silica film at the mica-waterinterface under the help of surfactant molecules [3]. Later, a differentsolution route to making a mesoporous FSM of anatase nanocrystalliteshas been developed [4]. Thereafter, fabrications of functional FSMsusing 1D inorganic nanostructures have been discussed more often inliterature. Recently, nanofibers of microporous manganese oxides havebeen cast into a paper-like FSM with a precisely controlledlayer-by-layer alignment for the nanofibers [5]. Sheets of entangledV₂O₅ nanofibers were made to have the high Young's modulus, largeactuator-generated stress, and significant actuator stroke at lowapplied voltage [6]. In addition, carbon nanotubes (CNT) have been usedfor fabricating functional FSMs. The buckypaper containing coaxialcarbon nanotubes with improved mechanical property, thermalconductivity, and structural stability has been first reported [7].Lately, strong, transparent, and multifunctional sheets of orthogonallyorganized CNTs were made with the gravimetric strength better than thatof sheets of high-strength steel [8].

However, the abovementioned inorganic nanofiber FSMs may not be stableduring a prolonged heating in air above 550° C. [5]. CNTs, on the otherhand, may be fast oxidized in such a harsh calcination. Thus, thedevelopment of a thermal stable and chemically inert TiO₂-basednanofiber FSM would be of great interest for advancing the existingtechnologies in high temperature catalysis, sensing, sorption andseparation. Furthermore, large scale fabrication of robust,thermal-stable, and multifunctional macroscopic three-dimensional (3D)structures directly from the ID nanomaterials has remained as achallenge.

Therefore, a heretofore unaddressed need exists in the art to addressthe aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a method ofphotocatalytically decomposing organic pollutants. In one embodiment,the method includes the steps of mixing a solution containing organicpollutants and a plurality of TiO₂-containing, macro-sizednanostructures to form a mixture; and exposing the mixture to UVirradiation to decompose the organic pollutants, where the UVirradiation is emitted from an irradiation source that is positioned ata distance from the mixture.

In one embodiment, the plurality of TiO₂-containing, macro-sizednanostructures are provided in the form of a membrane or a sheet. Theorganic pollutants comprise a plurality of nerve agents (NA) or nerveagent simulants (NAS). In one embodiment, the nerve agent simulants(NAS) comprise diethyl phenylthiomethylphosphonate (DPTMP). The UVirradiation has a wavelength, λ, in the range of about 250 to 400 nm,and the exposure time of the mixture to the UV irradiation is in therange of about 1-60 minutes.

In one embodiment, the decomposition of the organic pollutants ischaracterized with a ratio, R=(1−C_(t)/C₀), where C₀ and C_(t) are themeasured concentration of the organic pollutants in the mixture beforeand after the exposing step, respectively, and R is in the range of fromzero to one, and where when R=0, no organic pollutants in the mixtureare decomposed, and when R=1, the organic pollutants in the mixture arecompletely decomposed after the exposing step.

The method also includes the steps of soaking the membrane or sheet in avolume of an Mg(NO₃)₂ solution at room temperature (RT) for a firstperiod of time; and drying the membrane or sheet at RT; and heating thedried membrane or sheet in air at a temperature in the range of about 25to 300° C. for a second period of time. In one embodiment, the firstperiod of time is in the range of about 0.1 to 15 hours, and the secondperiod of time is in the range of about 0.5 to 5 hours.

The method further includes the steps of measuring the concentration ofthe organic pollutants in the mixture before and after the exposingstep. Each measuring step is performed with a UV-visible spectrometer

In another aspect, the present invention relates to a device ofphotocatalytically decomposing organic pollutants. In one embodiment,the device has at least one membrane or sheet formed withTiO₂-containing, macro-sized nanostructures; a container for receiving asolution containing organic pollutants and the membrane or sheet; and aUV irradiation source positioned at a distance from the container foremitting UV irradiation onto the solution.

The device further has a detector for measuring the concentration of theorganic pollutants in the solution. In one embodiment, the detectorcomprises a UV-visible spectrometer.

The organic pollutants comprise nerve agents or nerve agent simulants(NAS). In one embodiment, the nerve agent simulants (NAS) comprisediethyl phenylthiomethylphosphonate (DPTMP). The UV irradiation has awavelength, λ, in the range of about 250 to 400 nm, and where theexposure time of the solution to the UV irradiation is in the range ofabout 1-60 minutes.

In one embodiment, the TiO₂-containing, macro-sized nanostructures aresynthesized by mixing an amount of TiO₂ powders with a volume of analkali or alkaline solution to form a mixture; and heating the mixtureat a temperature higher than 160° C. for a period of time effective toallow TiO₂-containing, macro-sized nanostructures to form, where theTiO₂-containing, macro-sized nanostructures form in an environment thathas no presence of a substrate that comprises Ti. In one embodiment, theTiO₂-containing, macro-sized nanostructures comprise substantiallynanofibers or nanowires with a typical diameter in the range of about 20nm to 150 nm, where the nanofibers or nanowires are substantially in theTiO₂—B phase or titanate phase.

In one embodiment, the membrane or sheet comprises a layered structure.The TiO₂-containing nanostructures in each layer are at least partiallyintertwined, thereby forming a plurality of voids therein. The membraneor sheet is replacable by another membrane or sheet formed withTiO₂-containing, macro-sized nanostructures. In one embodiment, the atleast one membrane or sheet formed with TiO₂-containing, macro-sizednanostructures comprises a first membrane or sheet and a second membraneor sheet positioned apart from the first membrane or sheet. The membraneor sheet is disposable.

In yet another aspect, the present invention relates to a device usablefor filtering micrometer-sized particles, comprising one or more filtersmade with a plurality of TiO₂-containing nanostructures. The pluralityof TiO₂-containing nanostructures comprises TiO₂-containing nanofibers,nanowires, nanoriboons, nanobelts, nanobundles, or any combinations ofthem. In one embodiment, the TiO₂-containing nanofibers or nanowires aresubstantially in the TiO₂—B phase or titanate phase. In one embodiment,each of the one or more filters comprises a layered structure, and wherethe TiO₂-containing nanostructures in each layer are at least partiallyintertwined, thereby forming a plurality of voids therein.

In a further aspect, the present invention relates to athree-dimensional (3D) scaffold usable for directing the growth of stemcells, comprising a body portion formed with TiO₂-containing,macro-sized nanostructures, where the body portion is at least partiallycoated with a plurality of biomolecules. In one embodiment, theTiO₂-containing, macro-sized nanostructures comprise substantiallynanofibers or nanowires with a typical diameter in the range of about 20nm to 150 nm, and where the plurality of biomolecules comprises growthhormone. The TiO₂-containing nanofibers or nanowires are substantiallyin the TiO₂—B phase or titanate phase.

In yet a further aspect, the present invention relates to a method ofwriting-erasing-rewriting information. In one embodiment, the methodincludes the steps of (a) providing a writing medium formed withTiO₂-containing, macro-sized nanostructures; (b) writing information onthe writing medium; (c) exposing the writing medium with the writteninformation to UV irradiation for a period of time so as to erase thewritten information on the writing medium; and (d) repeating steps (b)and (c) for a desired number of time.

In one embodiment, the TiO₂-containing, macro-sized nanostructurescomprise substantially nanofibers or nanowires with a typical diameterin the range of about 20 nm to 150 nm. The TiO₂-containing nanofibers ornanowires are substantially in the TiO₂—B phase or titanate phase. Inone embodiment, the writing medium comprises a paper-like film formedwith the TiO₂-containing nanofibers or nanowires.

In one aspect, the present invention relates to a writing medium forinformation storage, comprising a paper-like film formed withTiO₂-containing, macro-sized nanostructures, where the TiO₂-containing,macro-sized nanostructures comprise substantially nanofibers ornanowires with a typical diameter in the range of about 20 nm to 150 nm.In one embodiment, the TiO₂-containing nanofibers or nanowires aresubstantially in the TiO₂—B phase or titanate phase.

The writing medium is formed with TiO₂-containing, macro-sizednanostructures such that when the writing medium with visible writteninformation is subject to UV irradiation for a period of time, thewritten information on the writing medium becomes substantiallyinvisible. The writing medium is usable for rewriting with visibleinformation.

In another aspect, the present invention relates to a paper. In oneembodiment, the paper comprises a sheet formed with TiO₂-containing,macro-sized nanostructures. In one embodiment, the TiO₂-containing,macro-sized nanostructures comprise substantially nanofibers ornanowires with a typical diameter in the range of about 20 nm to 150 nm.The TiO₂-containing nanofibers or nanowires are substantially in theTiO₂—B phase or titanate phase.

In one embodiment, the paper is formed with TiO₂-containing, macro-sizednanostructures such that when the paper with visible written informationis subject to UV irradiation for a period of time, the writteninformation on the paper becomes substantially invisible. The paper isusable for writing or rewriting with visible information. In oneembodiment, the paper is usable for wall paper.

In yet another aspect, the present invention relates to a compositeusable for making tires. In one embodiment, the composite comprises aneffective amount of TiO₂-containing, macro-sized nanostructures and aneffective amount of rubber polymers, where the effective amount ofTiO₂-containing, macro-sized nanostructures comprises substantiallynanofibers or nanowires with a typical diameter in the range of about 20nm to 150 nm. In one embodiment, the TiO₂-containing nanofibers ornanowires are substantially in the TiO₂—B phase or titanate phase.

In a further aspect, the present invention relates to a multi-functionalvest/coat. In one embodiment, the multi-functional vest/coat comprises aplurality of TiO₂-containing, macro-sized nanofibers, where theplurality of TiO₂-containing, macro-sized nanostructures comprisesubstantially nanofibers or nanowires with a typical diameter in therange of about 20 nm to 150 nm. In one embodiment, the plurality ofTiO₂-containing nanofibers or nanowires is substantially in the TiO₂—Bphase or titanate phase. In one embodiment, the plurality ofTiO₂-containing nanofibers or nanowires is at least partiallyintertwined, thereby forming a plurality of voids therein. In oneembodiment, the plurality of TiO₂-containing nanofibers or nanowiresform a sensor, a drug releaser, a textile or a filter, where the sensor,the drug releaser, or the filter is controllable.

These and other aspects of the present invention will become apparentfrom the following description of the preferred embodiment taken inconjunction with the following drawings, although variations andmodifications therein may be affected without departing from the spiritand scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate one or more embodiments of theinvention and, together with the written description, serve to explainthe principles of the invention. Wherever possible, the same referencenumbers are used throughout the drawings to refer to the same or likeelements of an embodiment, and wherein:

FIG. 1 shows schematically a process of fabrication of a nanofiber cupaccording to one embodiment of the present invention;

FIG. 2 shows images of flexible nanofiber-based FSMs and cups fabricatedaccording to embodiments of the present invention: (a) a plane FSM and afolded FSM (inset), and (b) FSM cups made on a filter paper template anda plastic template (inset);

FIG. 3 shows images of SEM (scanning electron microscope), FESEM (fieldemission scanning electron microscope) and TEM (transmission electronmicroscope) images of a nanofiber FSM according to one embodiment of thepresent invention: (a) an SEM image of the cross-section of thenanofiber FSM showing a multi-layered texture, (b) a high resolutionFESEM image of the nanofiber FSM showing the intertwined nanofibers, and(c) a TEM image of the nanofibers of the nanofiber FSM;

FIG. 4 shows SEM, FESEM and TEM images of a calcined nanofiber FSMaccording to one embodiment of the present invention: (a) an SEM imageof the cross-section of the nanofiber FSM showing a multi-layeredtexture after the calcination at a temperature about 700° C., and (b) ahigh resolution FESEM image of the nanofiber FSM showing intertwinednanofibers after the calcination at a temperature about 700° C., and(inset) a TEM image of the calcined TiO₂ nanofibers, and (c) X-raypowder diffraction pattern of a paper of titanate nanofibers before andafter calcined at about 700° C. for about 3 hours;

FIG. 5 shows (a) a high resolution FESEM image of a nanofiber FSM havingthe intertwined nanofibers, and (b) images of nanofiber cups and tubesmade of the nanofiber FSM according to one embodiment of the presentinvention;

FIG. 6 shows photoassisted information writing-erasing on a nanofiberFSM paper according to one embodiment of the present invention and aregular printing paper, (a) the fourth writing of information on thenanofiber FSM paper and the first writing of information on the printingpaper using the ink of crystal violet, and (b) the fourth erasing ofinformation by the UV irradiation;

FIG. 7 shows photocatalytic decompositions of nerve agent simulants(NAS) by a TiO₂-containing FSM in water at RT according to twoembodiments (a) and (b) of the present invention;

FIG. 8 shows (a) an image of a nanofiber FSM having the TiO₂-containingnanofibers intertwined to form porous nets, and (b) schematically abacteria spores filter, according to one embodiment of the presentinvention;

FIG. 9 shows schematically an integration of the permeation and thephotocatalysis of a TiO₂-containing nanofiber membrane cup according toone embodiment of the present invention;

FIG. 10 shows the concentration of drug released by a TiO₂-containingnanofiber drug releaser in a solution according to one embodiment of thepresent invention; and

FIG. 11 shows schematically a multi-functional vest/coat made at leastpartially with the TiO₂-containing, macro-sized nanofiber fabricaccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the followingexamples that are intended as illustrative only since numerousmodifications and variations therein will be apparent to those skilledin the art. Various embodiments of the invention are now described indetail. Referring to the drawings of FIGS. 1-11, like numbers indicatelike components throughout the views. As used in the description hereinand throughout the claims that follow, the meaning of “a”, “an”, and“the” includes plural reference unless the context clearly dictatesotherwise. Also, as used in the description herein and throughout theclaims that follow, the meaning of “in” includes “in” and “on” unlessthe context clearly dictates otherwise. Moreover, titles or subtitlesmay be used in the specification for the convenience of a reader, whichshall have no influence on the scope of the present invention.Additionally, some terms used in this specification are morespecifically defined below.

DEFINITIONS

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the invention, and in thespecific context where each term is used.

Certain terms that are used to describe the invention are discussedbelow, or elsewhere in the specification, to provide additional guidanceto the practitioner in describing the apparatus and methods of theinvention and how to make and use them. For convenience, certain termsmay be highlighted, for example using italics and/or quotation marks.The use of highlighting has no influence on the scope and meaning of aterm; the scope and meaning of a term is the same, in the same context,whether or not it is highlighted. It will be appreciated that the samething can be said in more than one way. Consequently, alternativelanguage and synonyms may be used for any one or more of the termsdiscussed herein, nor is any special significance to be placed uponwhether or not a term is elaborated or discussed herein. Synonyms forcertain terms are provided. A recital of one or more synonyms does notexclude the use of other synonyms. The use of examples anywhere in thisspecification, including examples of any terms discussed herein, isillustrative only, and in no way limits the scope and meaning of theinvention or of any exemplified term. Likewise, the invention is notlimited to various embodiments given in this specification. Furthermore,subtitles may be used to help a reader of the specification to readthrough the specification, which the usage of subtitles, however, has noinfluence on the scope of the invention.

As used herein, “about” or “approximately” shall generally mean within20 percent, preferably within 10 percent, and more preferably within 5percent of a given value or range. Numerical quantities given herein areapproximate, meaning that the term “about” or “approximately” can beinferred if not expressly stated.

As used herein, the term “photocatalysis” refers to a process of theacceleration of a photoreaction in the presence of a photocatalyst. Whena photocatalyst TiO₂ captures ultraviolet light (UV) either from sun orfluorescent light, it forms activated oxygen from water or oxygen in theair. This process is similar to photosynthesis, in which chlorophyllcaptures sunlight to turn water and carbon dioxide into oxygen andglucose. The formed activated oxygen is strong enough to oxidize anddecompose organic materials, pollutants or smelling gas, and killbacteria.

OVERVIEW OF THE INVENTION

Making large-scale, multifunctional, paper-like FSMs and the FSM-based3D macroscopic devices purely from long inorganic functional nanowiresis challenging in many nanomaterial systems. The present invention,among other things, discloses methods of synthesis of macro-sizednanostructures and direct fabrications of FSMs and FSM-based 3D devicesusing the macro-sized nanostructures, and also potential applications inphotocatalysis, writing-erasing-rewriting information, microfiltration,controlled drug release, and the likes.

The description will be made as to the embodiments of the presentinvention in conjunction with the accompanying drawings of FIGS. 1-11.In accordance with the purposes of this invention, as embodied andbroadly described herein, this invention, in one aspect, relates to amethod for synthesizing TiO₂-containing, macro-sized nanostructuresincluding nanofibers, nanotubes, nanowires, or any combination of them.

According to the present invention, in one embodiment, TiO₂-containing,macro-sized nanostructures are synthesized by mixing an amount of TiO₂powders with a volume of an alkali or alkaline solution to form amixture that is contained in a containers and sealed therein, placingthe sealed container containing the mixture in an oven for heating, andthen heating the mixture therein at a temperature higher than 160° C.for a period of time effective to allow TiO₂-containing, macro-sizednanostructures to form. In one embodiment, the temperature for heatingthe mixture is in the range of about 180-300° C., and the period of timeof heating is in the range of about 3-960 hours. The formedTiO₂-containing, macro-sized nanostructures is then washed withdistilled water or a dilute acid.

The alkali solution can be one of NaOH, p KOH, LiOH, RbOH, CsOH, and anycombinations of them. The alkaline solution can be one of Mg(OH)₂,Ca(OH)₂, Sr(OH)₂, Ba(OH)₂, and any combinations of them.

According the present invention, the TiO₂-containing, macro-sizednanostructures are formed in an environment that has no presence of asubstrate that comprises Ti, such that the TiO₂-containing, macro-sizednanostructures comprise substantially nanofibers with a typical diameterin the range of about 20 nm to 150 nm and a typical length in the rangeof about hundreds of micrometers to few millimeters, as shown in FIGS. 3and 4, for example. The nanofibers are substantially in the TiO₂—B phaseor titanate phase.

Conventionally, TiO₂-containing nanostructures are produced by treatingthe TiO₂ powders in a concentrated solution of NaOH at a temperatureabout 150° C. [10] or lower temperatures. The nanostructures were formedon a substrate that is seeded with TiO₂ powders. The resultantnanostructures comprise substantially nanotubes that are typically aboutseveral to tens of micrometers in length.

The synthetic process of the TiO₂-containing, macro-sized nanostructuresaccording to the present invention, however, requires the heatingtemperature be greater than 160° C. for a period of time effective toallow TiO₂-containing, macro-sized nanostructures to form, and thereforeresults in macro-sized nanofibers about hundreds of micrometers to fewmillimeters in length, where the macro-sized nanofibers grow in anenvironment that has no presence of a substrate that is seeded with TiO₂powders. For example, in one embodiment, the macro-sized nanofibers weresynthesized by first adding about 0.3 g of the TiO₂ powders (DegussaP25) into about 40 mL of 10 M alkali or alkaline solution in a 150 mLTeflon-lined autoclave container. The container was then sealed andheated in an oven for about 1-7 days at a temperature substantiallyabove 160° C. for the growth of macro-sized nanofibers in length. Othercontainers can also be used to practice the current invention. After thereaction (growth), the synthesized nanofibers were washed with distilledwater. The synthesized nanofibers were white and pulp-like and could beused to form FSMs and/or 3D structures including cups and tubes.

In another aspect, the present invention relates to TiO₂-containing,macro-sized nanostructures synthesized according to the above method.

In yet another aspect, the present invention relates to a syntheticnanostructure. The synthetic nanostructure includes a reaction productof a chemical reaction according to the formula of:2NaOH+3TiO₂=Na₂Ti₃O₇+H₂O,where the chemical reaction takes place at a temperature higher than160° C. for a period of time effective to allow the reaction product toform, and furthermore, the chemical reaction takes place in anenvironment that has no presence of a substrate that comprises Ti. Inone embodiment, the chemical reaction takes place in a sealed container.The effective temperature is in the range of about 180-300° C. Theeffective period of time is in the range of about 3-960 hours.

A first reactant TiO₂ is provided in the form of powders, and a secondreactant that comprises an inorganic base is provided in the form ofsolution. In one embodiment, the second reactant comprises NaOH and thereaction product comprises a compound of the formula Na₂Ti₃O₇. Thecompound of the formula Na₂Ti₃O₇ is in the form of nanofiber with atypical diameter in the range of 20 nm to 150 nm.

The synthesized nanofibers can be used to form 2D FSMs and/or 3Dstructures including cups and tubes.

For example, a two-dimensional (2D) FSM can be formed by the followingsteps: at first, a plurality of TiO₂-containing, macro-sizednanostructures are provided. Then the plurality of TiO₂-containing,macro-sized nanostructures is cast over a template film to form a freestanding membrane over the template film. Next, the free standingmembrane cast over the template film is dried at a temperature for aperiod of time. The temperature of drying is substantially in the rangeof about 0-180° C. The period of time of drying is substantially in therange of about 0.5-30 hours. Finally, the dried free standing membraneis removed from the template film by calcining the dried free standingmembrane over the template film at a temperature in the range of300-600° C. for the template film of an ashless filter paper, or by handfor the template film of a polyethylene film. The template film issubstantially 2D.

The casting step has the steps of casting a first plurality ofTiO₂-containing, macro-sized nanostructures over the template film;drying the first plurality of TiO₂-containing, macro-sizednanostructures cast over the template film at RT for a first period oftime; subsequently casting at least one additional plurality ofTiO₂-containing, macro-sized nanostructures over the dried firstplurality of TiO₂-containing, macro-sized nanostructures cast over thetemplate film; and drying the at least one additional plurality ofTiO₂-containing, macro-sized nanostructures cast over the dried firstcollection of TiO₂-containing, macro-sized nanostructures cast over thetemplate film at RT for a second period of time that is substantiallydifferent from or equal to the first period of time.

Accordingly, the 2D FSM is formed with multi-layers and has a thicknessin a range of from tens to hundreds of micrometers. The thickness of the2D FSM is determined by the amount of TiO₂-containing, macro-sizednanostructures cast over the template film. The TiO₂-containingnanofibers in each layer are at least partially intertwined, therebyforming voids therein. The 2D FSM is porous, permeable and zeolitic,chemically inert, biocompatible, and/or thermally stable, as shownbelow.

The above disclosed procedures can also be utility to fabricate a 3Dstructure directly from nanostructures. In this case, a template havinga 3D configuration corresponding to the 3D structure to be formed isutilized, instead of a 2D film. Accordingly, the 3D structure has a wallportion formed with multi-layers. The TiO₂-containing nanofibers in eachlayer are at least partially intertwined, thereby forming voids therein.The wall portion of the 3D structure has a thickness in a range of fromtens to hundreds of micrometers. At least a portion of the 3D structureis porous, permeable and zeolitic. The 3D structure is chemically inert,biocompatible, and/or thermally stable.

Referring to FIG. 1, a process 100 for forming a nanofiber cup 150 isschematically shown according to one embodiment of the presentinvention. At first, a macroscopic template or mold 110 is provided. Themacroscopic template or mold 110 has a desired 3D structure and size andis made of an ashless filter-paper, a polyethylene film, or othermaterials. Then the macro-sized nanofibers synthesized according to theinvented method(s) disclosed in this specification are cast over themacroscopic template or mold 110. The cast nanofiber cup 150 cast overthe macroscopic template or mold 110 is dried at a temperature in therange of about 0-180° C. in an oven for the period of time in the rangeof about 0.5-30 hours. Thereafter, the template or mold 110 is simplyremoved by hand for a plastic template or burning out via thecalcination at a temperature about 500° C. for a filter paper template,thereby resulting in the nanofiber cup 150 made of the inorganicnanofibers. The wall (membrane) thickness of the nanofiber cup 150varies from tens to hundreds of micrometers, depending on the amount ofthe nanofibers used.

In one aspect, the present invention relates to a syntheticnanostructure. In one embodiment, the synthetic nanostructure includes areaction product of several chemical reactions in sequence according tothe formulae of:2NaOH+3TiO₂→Na₂Ti₃O₇;  (a).Na₂Ti₃O₇+2H⁺→2Na⁺+H₂Ti₃O₇; and  (b).H₂Ti₃O₇→H₂O+TiO₂—B,  (c).where at least chemical reaction (a) takes place at a temperature higherthan 160° C. for a period of time effective to allow the reactionproduct to form, and furthermore, the at least chemical reaction (a)takes place in an environment that has no presence of a substrate thatcomprises Ti. In one embodiment, the effective temperature is in therange of about 180-300° C. The effective period of time is in the rangeof about 3-960 hours.

In one embodiment, a first reactant TiO₂ is provided in the form ofpowders, and a second reactant that comprises an inorganic base isprovided in the form of solution. The second reactant in one embodimentcomprises NaOH. In another embodiment, the second reactant comprisesOH⁻. The reaction product comprises a compound of the formula Na₂Ti₃O₇.The compound of the formula Na₂Ti₃O₇ is in the form of macro-sizednanofibers with a typical diameter in the range of 20 nm to 150 nm.

In one embodiment, at least chemical reaction (a) takes place in asealed container. Chemical reaction (b) takes place substantiallybetween 180° C. and 300° C. for a period of time effective to allow thecompound of the formula H₂Ti₃O₇ to form in the form of macro-sizednanofibers. Chemical reaction (c) takes place in a calcination process,where the calcination process can be a step of heating in a furnace at atemperature in the range of 300-600° C. in air and a step of burning inair.

The chemical reaction (c) causes the compound of the formula TiO₂—B toform in the form of macro-sized nanofibers, where the compound of theformula TiO₂—B as formed in the form of macro-sized nanofibers is with atypical diameter in the range of 20 nm to 150 nm.

In addition, the present invention can find many applications in a widespectrum of fields, such as:

-   -   (1). membrane catalysts (no binders/supports/down-stream        separations),    -   (2). catalytic supports (membrane macropores support catalyst        particles),    -   (3). catalytically decomposing pollutants, e.g., nerve agents,        in water under UV light, about 12 times more powerful than the        commercial TiO₂ powder,    -   (4). drug delivery (DNA, protein, and organic drugs can be        stored in the voids or macropores for slow or controlled        releases),    -   (5). tissue regeneration (tissue cells can grow in the        biocompatible voids),    -   (6). solar cell and water photo-splitting,    -   (7). oil cracking,    -   (8). making and storing hydrogen for fuel cells,    -   (9). writing-erasing-rewriting of information,    -   (10). making multi-functional vests/coats for nanomedicine,        battlefield and firefighter, etc., and    -   (11). making tire for vehicles.

These and other aspects of the present invention are more specificallydescribed below.

IMPLEMENTATIONS AND EXAMPLES OF THE INVENTION

Without intent to limit the scope of the invention, exemplary methodsand their related results according to the embodiments of the presentinvention are given below. Note that titles or subtitles may be used inthe examples for convenience of a reader, which in no way should limitthe scope of the invention. Moreover, certain theories are proposed anddisclosed herein; however, in no way they, whether they are right orwrong, should limit the scope of the invention so long as the inventionis practiced according to the invention without regard for anyparticular theory or scheme of action.

Example 1

Synthesizing TiO₂-containing, Macro-sized Nanofibers/Nanowires andFabricating FSMs and 3D Devices: According to the present invention, asynthetic route for the hydrothermal synthesis of TiO₂-containing,macro-sized nanofibers/nanowires at an effective temperature above 160°C. for an effective time period is disclosed.

In this exemplary embodiment, about 0.30 g of TiO₂ powder (Degussa P25)was introduced into about 40 mL of 10 M alkali solution in a 150 mLTeflon-lined autoclave container. The container was then sealed andplaced in an oven for heating. After the hydrothermal reaction in theoven a temperature above 160° C. for about 7 days, a white pulp-likeproduct of the TiO2-containing, macro-sized nanofibers was collected,washed with distilled water or a dilute acid. The washed white pulp-likeproduct of the TiO2-containing, macro-sized nanofibers was cast on amacroscopic template made of either an ashless filter-paper (Whatman) orpolyethylene film, and then dried at RT. This casting-drying process wasrepeated for several times at RT, and followed thereafter by a heatingat about 0-180° C. in an oven for about 0.5-30 hours. Accordingly, a 2DFSM paper or a 3D cup was formed with the TiO₂-containing, macro-sizednanofibers on the macroscopic template. Then the macroscopic templatewas removed from the 2D FSM paper or the 3D cup. In this example, themacroscopic template includes a plastic plate or a cup.

Referring to FIGS. 2 a and 2 b, images of the nanofiber FSMs 210 and220, and nanofiber membrane cups 250 and 260 are shown, respectively.FIG. 2 a displays a plane FSM 210 and a folded FSM 220. The membranesize can be varied from several to tens of centimeters, depending on theamount of the nanofiber used. In practice, it has been noticed thatslowly deposited FSMs easily survived from multiple bends and folds,revealing the robust nature of the paper-like FSM formed typically bylong and flexible fibers and indicating that a longer time for thenanofibers to settle on (cast over) the template would substantiallyincrease the robustness of the FSM. The correlation between thedeposition time and the membrane flexibility (or robustness) impliedthat the FSM formation process was accompanied by a self-assembly of thenanofibers. The settling time was controlled by either the ratio ofwater to the nanofibers or the temperature for drying the nanofibers, ora combination of both. Inset in FIG. 2 a demonstrates that the plane FSM210 could be readily folded like a piece of paper to form a folded FSM220, reflecting a flexible nature of the FSM formed by the long(macro-sized) nanofibers. The 1D nanostructure self-assembly is alsoshown in FIG. 14. For comparison, the image of a one cent coin 230 isalso shown in FIG. 2 a.

A systematic study on varying the fabrication parameters has suggestedthat the FSM paper's flexibility could be controlled by optimizing (a)the ratio of water to the nanowires in the pulp and (b) the time fordrying the nanowire pulp. The preparation of such robust FSM has enabledone to directly cast the long nanowires, under the help of the 3Dtemplates or molds, into macroscopic 3D devices such as tube, bowl, andcup, as shown in FIG. 2 b. Such nanowire membrane devices, each weighingabout 0.2-0.3 g and with a nearly 500 μm wall thickness, can be freelyhandled by hands and trimmed with scissors, which is among the firstattempts to cast at RT a pure inorganic nanofiber-containing 3D ceramicdevice that can be cut by scissors.

As shown in FIG. 2 b, macroscopic membrane nanofiber cups 250 and 260were formed by casting the nanofibers over templates of an ashlessfilter-paper and a polyethylene film, respectively. The plastic templatewas detached by hand. The filter-paper template, however, was removed bythe calcination at a temperature about 500° C. or burnt out by openflames in air. The macroscopic membrane nanofiber cups 250 and 260 werewhite, weighing about 0.3 grams. Such inorganic nanofiber vessels weredifferent from those cast by the traditional ceramic engineeringprocesses involving a firing at the temperatures near or above 1,000° C.For comparison, the image of a one cent coin 240 is also shown in FIG. 2b.

The successful casting of the FSMs or 3D membrane devices would dependon the morphology and spatial organization of the nanofibers. The longnanofibers can self-organize into the robust FSM and 3D membrane deviceswhile nanoparticles or short nanofibers cannot. Further, the controlledassemblies of the nanofibers can determine the robustness of the 3Dmembrane device.

Surface morphologies and lateral structures of the TiO₂-containing,macro-sized nanofibers, the free standing membrane and 3D devices of thenanofibers according to embodiments of the present invention werecharacterized by means of a transmission electron microscope (TEM), ascanning electron microscope (SEM), and a field emission scanningelectron microscope (FESEM), energy-dispersive X-ray analyses (EDX), andX-ray diffraction (XRD), respectively. The SEM and EDX work was done ona Philips ESEM XL30 microscope. The XRD data were collected on a PhilipsX'Pert X-ray diffractometer. The TEM study was carried out on a JEOLX-100 microscope and JEOL 2010 FEG STEM/TEM.

The SEM, FESEM and TEM images of the wall portion of a nanofiber cupaccording to one embodiment of the present invention were shown in FIGS.3 a-3 c, respectively. As shown in FIG. 3 a, the wall portion of thenanofiber cup was formed with multi-layers of self-aggregatednanofibers. The number of the layers was in line with the number oftimes that the nanofibers had been added on the template. Themulti-layer structure of the cup membrane indicated that the air-dryingprocess was accompanied by a spontaneous self-organization for thenanofibers. The nanofibers shown in FIG. 3 a were less organized thanthose reported in literature [5, 8]. But, it could be anticipated thatthe nanofibers' organization would be improved by allowing a longer timefor the self-organization at an elevated temperature, or by employingspecial techniques such as the “nano-logging” [11], magnetic fieldalignment [12], etc.

A high resolution FESEM photographic image of the cup wall portion shownin FIG. 3 b revealed the microscopic details of the entangled nanofibersin the cup membrane, thereby forming 3D voids therein. The nanofibershad the diameters ranging from about 50 nm to about 100 nm, and thelengths most near about 1 mm or longer. Certain nanofibers, however, hadthe lengths about tens to hundreds of micrometers due probably to acontinuous nucleation and/or an uneven growth commonly seen in aprolonged hydrothermal heating. The nanofibers in the cup wall portionwere intertwined, thereby forming the 3D porous FSM with a controlledthickness about 0.1 mm. The thickness may be varied with the amount ofnanofibers used. The 3D voids, about 0.5 to 10 micrometers in size,would be ideal for the nanofibers to expand during the heating or tomove around in response to a mechanical stress, thus improving thethermal stability and mechanical strength of the FSM. Practically, these3D macropores are useful for fast mass transport in catalysis and gasstorage over a wide temperature range, thus differentiating this FSMfrom those reported elsewhere.

FIG. 3 c was a TEM image of the nanofibers in the cup wall portion shownin FIG. 3 b. As shown in FIG. 3 c, the average diameter of thenanofibers was about 60 nm. Moreover, no nanotubes could be seen in thissample under the TEM. This result was in line with what had beenreported in literature that the heating temperature higher than 160° C.in the hydrothermal synthesis would mainly result in nanofibers ratherthan nanotubes [13]. As disclosed above, the hydrothermal heatingtemperatures above 160° C. were employed in the present invention forthe purpose of forming the pulp-like and long nanofibers.

XRD patterns of the nanofibers confirm that the 1D nanowire samplesresemble the titanate in lattice structure [13]. The XRD data havesuggested that thus-formed nanowires should be the titanate phase, whichis characterized by the following lattice parameters: [2θ=9.8° (001),11.2° (200), 24.4° (110), and 29.7° (003), (JCPDS card No.: 47-0561)].The titanate structure's basic building unit is a TiO₆-octahedron [22].The edge-shared (TiO₆) octahedra would form a negatively charged layeredstructure. The countercations (e.g., Na⁺) sit in between the adjacentlayers, thus resulting in variable interlayer distances depending on thesize and the hydration degree of the cation, which would explain theflexibility of the long nanofibers [23].

The thermal stability of the nanofiber FSM was investigated by heatingthe membranes at temperatures above 500° C. in air for three hours. FIG.4 a shows that the inorganic nanofiber FSM retained the typicalmulti-layered texture after 3 hours of the calcination in a furnace at atemperature about 700° C. in air. FIG. 4 b displays a FESEM picture forthe inorganic nanofiber FSM after the calcination at a temperature about700° C., showing clearly the fibrous nanostructures identical to thoseshown in FIG. 3 b. Same results were obtained from samples beingcalcined at a temperature about 600° C. The TEM image in the inset ofFIG. 4 b demonstrates that the calcined FSM was mainly composed of thenanofibers with the same structure shown in FIG. 3 c. After beingcalcined for 3 hours at a temperature about 800° C., however, themembrane nanofibers became much shorter and thicker than before, makingthe FSM no longer flexible that in turn suggested that the nanofiberstructure experienced a phase transformation at about 800° C.

As shown in FIGS. 4 a and 4 b, after the 3 hours calcination period at700° C. in air, the wall portion of the 3D objects still retained thecharacteristic multidecker structure of the entangled nanowires. Afterthe calcination at 800° C., however, the wall membrane became brittle.This is because the original nanowire morphology has changed to one thatis typically 20 μm long and 100-400 nm wide. The XRD data suggested thatthe nanowires should be in the TiO₂—B phase, which is characterized bythe following lattice parameters: (a=12.1787, b=3.7412, c=6.5249 Å;β=107.0548°) after the calcination at 700° C., and then a mixture ofTiO₂—B and anatase after the calcination at 800° C. Both XRD patternsagree well with the results reported in the literature [24]. Beingdifferent from other paper-like materials [6-8], this macroporousnanowire paper could be very useful in high-temperature catalysis. FIG.4 c shows an X-ray powder diffraction pattern of a paper of theTiO₂-containing long nanofibers before (410) and after (420) calcined atabout 700° C. for about 3 hours.

FIG. 5 a shows a high resolution FESEM image of a nanofiber FSM havingthe intertwined nanofibers. FIG. 5 b shows images of various 3Dstructures such as nanofiber cups 550 and 560 and tube 570 in comparisonwith an image of one cent coin 530 according to embodiments of thepresent invention.

Briefly, the present invention, among other unique things, disclosesmethods of synthesizing TiO₂-containing, macro-sized nanofibers andfabricating thermal-stable, robust, and multifunctional FSM-based 2Dpaper and 3D devices (e.g., tube, bowl, cup and so on) in nearly anymacroscopic size and shape. Making long 1D nanostructures and thenorganizing them properly is critical in casting robust 2D FSMs directlyout of the 1D nanomaterials. The inorganic 1D nanostructure is white,thermal stable, chemically inert, biocompatible, and capable of formingflexible mm-long nanofibers with the typical diameter less than 100 nm.Such inorganic nanofibers can form conformal membranes on macroscopictemplates or molds of nearly any size for casting macroscopic vesselsand tools by design. The nanofibers have attracted wide attentions dueto their unique potentials in a wide range of applications includingchemical sensing, photocatalysis, photovoltaics, varistors, gas sensors,and solar cells [9]. The nanofiber FSM and cup vessels are easily scaledup, and ideal for mass productions due to the use of the inexpensive rawTiO₂ material. Due to the known thermal stability and chemicalinertness, such inorganic nanofiber FSM catalysts can be recyclable andreusable over a wide temperature range. The cast inorganic nanofiberFSMs, vessels, and tools may find uses in hydrogen storage [18] andgeneration [19], environmental cleaning [20], sensing [21],catalytically splitting water and cracking oil, making protection maskand armor, fabricating flame-retardant fabric, filtering bacteria,photoassisted rewriting, controlled drug releases, and regeneratingtissues, and the likes.

Example 2

An immediate application of the TiO₂-containing, macro-sized nanofibersis to provide a writing-erasing-rewriting function for informationstorage under the help of the UV irradiation. TiO₂ is commonly utilizedas an inexpensive and nontoxic photocatalyst. After being excited by UVlight, the TiO₂ can catalyze dye degradation [25].

In this example, four characters, “UARK”, of water-based ink (1.0×10⁻²mol/L crystal violet) were written on a FSM paper 610 made of theTiO₂-containing, macro-sized nanofibers according to the presentinvention. The FSM paper 610 with the written information of “UARK” wasexposed to the UV light in air. After 15 minutes of exposition to the UVlight, all the four characters “UARK” were disappeared, as shown in FIG.6 b. This writing-erasing cycle had been repeated for four times on theFSM paper 610 (21.4 mg) in the example, all the four characters “UARK”were erased for each time after it was exposed to the UV light, as shownin FIG. 6 b. For a regular printing paper 620, however, the UVirradiation in each time caused little change to the same charactersthat were written on the regular printing paper 620 (49.0 mg) in thefirst cycle. In addition, such inorganic nanofiber paper can bepotentially useful in many harsh environments below 700° C.

Yearly, about 9.5 million hectares are deforested globally, and 35% ofcommercial wood is used for paper production [26]. Therefore, use ofsuch rewritable, erasable, and heat-resistant inorganic nanofiber ornanowire paper might help save the disappearing forests.

Example 3

Another application of the TiO₂-containing, macro-sized nanofibers is inphotocatalysis. The catalytic activity of the TiO₂—B phase has beendemonstrated to be better than that of other TiO₂ phases [27]. Due toits macroporous nature, such robust nanowire-based membrane catalystsshould have unique potentials for photocatalytic decom-positions oforganic pollutants [15] such as nerve agent simulants (NAS) [15], forexample, (C2H5O)2P(O)(H2CSC6H5) (Aldrich).

In this exemplary embodiment, about 10 mg of the FSM made of theTiO₂-containing, macro-sized nanofibers according to the presentinvention was soaked in about 10 mL of 1 mol/L Mg(NO₃)₂ solution at RTfor about 12 hours. The soaked FSM was dried at RT, and then heated at atemperature above 100° C. for about 3 hours in air. The heated FSM isthen placed in a solution containing a number of organic pollutants. Inthe example, the organic pollutants comprise NAS. A UV lamp Entella(model B100 AP/R) was positioned about 5 mm above the solution with theFSM for VU irradiation the solution. The concentrations (C_(t)) of theNAS were measured on a UV-visible spectrometer, for example, HP 8453(Hewlett-Packard, Co.).

After a 15 minute UV irradiation on the solution having the nanowire FSMat RT, the NAS concentration (C_(t)) was reduced by 67.8%, (1−C_(t)/C₀),from the initially NAS concentration (C₀) (about 50 mL, and 4.5×10⁻⁷mol/L originally). The decomposition rate (1−C_(t)/C₀) of the NASconcentration in the case is indicated by bar 712 of FIG. 7 a, which isdifferent from the literature results [17].

The spectroscopic measurements of the NAS concentrations were performedon the HP 8453 UV-visible spectrometer. Without the catalyst of the FSM,the NAS concentration decrease after the same UV irradiation was lowerthan the detection limit. Another blank test, using this FSM without theUV irradiation, caused the NAS concentration, as indicated by bar 718 ofFIG. 7 a, to decrease by about 1.0%, implying that nearly 66.8% of theNAS concentration drop (67.8%-1.0%) mainly attributes to thephotocatalytic decomposition rather than the surface adsorption on thecatalyst.

In the TEM/SEM/XRD studies, no MgO nanoparticles could be seen on thenanofiber catalyst. The EDX study, however, shows that about 0.85 wt %of the Mg element exists in this catalyst. Both results have impliedthat the Mg species would likely be in a form of highly dispersedcluster(s), which encourages one to do the HRTEM work to identify theshape/size and then the role of the Mg-containing particles in thisphotocatalysis.

Parallel tests using the P25 and anatase TiO2 powder (325 mesh, AlfaAesar) of the same weight resulted in the reduction of the NASconcentration by 35.0% and 8.0%, as indicated by bars 714 and 716 ofFIG. 7 a, respectively. The FSM membrane is evidently far superior tothe P25 and anatase powders in the NAS photodecomposition, suggestingthat the nanowire FSM membrane could be an exciting new photocatalyst.During the UV irradiation, the solution temperature increase wasnegligible. In heterogeneous catalysis, utilizations of such nanowireFSM catalysts could minimize (i) the downstream separation and weightloss of catalysts, (ii) the use of catalytic supports and binders, and(iii) the cost due to the ease of recycling the catalyst via thecalcination.

Example 4

As disclosed in EXAMPLE 3, TiO₂ is superb in photocatalyticallydecomposing organic pollutants including the nerve agent simulants (NAS)[15]. This is different from the catalyses on activated carbons [16]that have the dark color. Additionally, the TiO₂ photocatalytic activitycan be greatly enhanced by the presence of Mg(II) [17]. In thisexemplary study, the photocatalytic properties of the nanofiber FSM werestudied at the RT in the aqueous solutions of the NAS that was thediethyl phenylthiomethylphosphonate (DPTMP, C₁₁H₁₇O₃PS) (Alfa Aesar).

Prior to the catalysis, the nanofiber FSM was firstly pretreated througha soaking in the solution of about 1 mol/L Mg(NO₃)₂ for about 12 hoursat RT, then dried at RT and heated in air at a temperature above 100° C.for about 3 hours. The NAS solution was prepared by dissolving about 45μmol of the DPTMP into about 100 mL water containing about 10 mg of thepretreated FSM. After a 15-min UV radiation from a lamp (MineralightUVGL-58, λ=254 nm) that was positioned about 5 mm above the solution,the NAS concentration (C_(t)) in the solution was reduced by 98%(1−C_(t)/C₀), as indicated by bar 722 of FIG. 7 b. The C_(t)measurements were conducted on the HP 8453 UV-visible spectrometer. Ablank test using the pretreated FSM of same weight without the UVradiation showed that the NAS concentration was decreased by only 1%, asindicated by bar 728 of FIG. 7 b, which suggested that the NASconcentration drop of 98% was mainly due to the photocatalyticdecomposition rather than the surface adsorption on the nanofibers. Inparallel, the anatase TiO₂-powder (325 mesh, Alfa Aesar) of the sameweight after the same pretreatment was used in this catalysis, resultingin a drop of the NAS C_(t) by 8%, as indicated by bar 726 of FIG. 7 b.No change in the solution temperature was observed after the UVradiations.

This 98% catalytic conversion may be further improved by theoptimizations of the reaction temperature, the time and the intensity ofthe UV radiation, and the structure and morphology as well as loading ofthe Mg-species. This 98% conversion is among the highest in the fastphotocatalytic decomposition of the NAS in water at RT, indicating anunusual potential of the nanofiber FSM catalysts for making, forinstance, new masks in civil defense applications. In comparison withthe common practice in heterogeneous catalyses, uses of the nanofiberFSM catalysts can minimize the downstream recovery of the powderycatalysts and at the same time eliminate the use of the catalyticsupports and binders. In addition, a more efficient use of the surfaceof each catalytic nanofiber, a negligible weight loss of the catalyst,and reuses of the catalyst through the high-temperature calcinationcould all be expected. A further detailed development on controlling thestructure, size, and dispersion of the Mg-species on the nanofibers,together with the optimization of the FSM porosity could lead to thedevelopment of new inorganic nanofiber membrane catalysts for a varietyof important catalysis-related applications.

Example 5

The nanofiber FSMs and 3D devices according to the present invention canfind applications in the filtration of particles. In this example,aqueous suspensions of polystyrene latex microspheres including AlfaAesar microspheres with 0.75, 1, 2, and 2.5 μm in diameter were providedfor investigating the permeability of the nanowire membrane [5]. Eachaqueous suspension had a concentration of 0.0025% (wt). Themicrofiltration using a TiO₂-containing nanofiber cup (filter) wasconducted within about 5 minutes. It had been shown that no 2-μmmicrospheres were detected in about 1 mL of the filtered sample (aqueoussuspension). Those of 0.75 μm and 1 μm microspheres, however, penetratedthe wall of the filter in the parallel tests, suggesting asize-exclusion function of the 3D devices in filtrations ofmicrometer-sized particles.

Furthermore, the TiO₂-containing nanofiber membrane can be used forfiltrations of bacteria spores in civil defense, environmental cleaning,neuron growth media to repair injured spinal cord, treatments ofAlzheimer's and Parkinson's diseases, inject-able bone repair, portableMEMS (Micro Electro Mechanical Sensor) biosensors and membranechem-sensors. FIG. 8 a shows an image of a nanofiber FSM having theTiO₂-containing nanofibers intertwined to form porous nets, which isused for the filtration of particles. FIG. 8 b shows schematically abacteria spores filtration using intertwined nanofibers.

Example 6

The unique integration of the permeation and the photocatalysis of ananofiber membrane cup 910 according to the present invention weredemonstrated in this example, as shown in FIG. 9. In this embodiment,the TiO₂-containing nanofiber membrane cup 910 was pretreated in aMg(II) solution according to the method as shown in EXAMPLES 3 and 4,and then was filled with a NAS solution 920. The cup 910 containing theNAS solution 920 was irradiated by a UV light 930 emitted for a UV lamp(Entela, model B100 AP/R) from one side of the cup 910, as shown in FIG.9. After 15 minutes of the UV irradiation, about 3.0 mL of thepermeated-catalyzed solution was collected, with (32.0±1.0) % of the NASinstantly decomposed. If a circular UV lamp could be utilized around thecup 920, the concentration reduction could be comparable to that in theFIG. 7 b (FSM/UV). This result demonstrates an application potential ofthe 3D devices in the industrial continuous flow-filtration-catalysis atdifferent temperatures, where the reactant-catalyst contact time islimited.

Example 7

Macroporous 3D devices, walled by the scaffolding nanowires/nanofibers,are useful in controlling drug release [29]. In the exemplary example, asection of the TiO₂-containing nanofiber FSM (74.0 mg) was pre-soaked inabout 100 mL solution of about 0.001 mol/L crystal violet for about 12hours at RT, and then placed in about 10 mL of fresh water at RT. Thecontrolled drug release was monitored by the HP 8453 UV-visiblespectrometer. After every 24 hours of the drug release, theTiO₂-containing nanofiber FSM was transferred into another 10 mL offresh water. FIG. 10 shows the concentration of drug released from theTiO₂-containing nanofiber FSM in the solution, which indicated that thecontrolled drug release reached a maximum at about 24 hours, and waseffective for at least 4 days.

Example 8

Furthermore, the 3D scaffolds of the TiO₂-containingnanofiber/nanowires, after being coated with growth hormone, is veryuseful in directing the growth of stem cells for potential applicationsin regenerative medicine [30, 31].

Example 9

Ceramic titanate nanowire (NW) is environmentally benign, biocompatible,chemically inert, surface functionalization easy, inexpensive, andthermally stable. In this example, a new composite is formed and usablefor making tires. The new composite comprises TiO₂-containing,macro-sized nanowires/nanofiber that are blended with rubber polymer. Incomparison with the carbon black-based rubber composite, the NW-rubbercomposite can be grey in color, and may provide the new tire with betterinterfacing with polymer backbone, higher mechanical strength andlighter in weight or better gas mileage, and easier in handling on wetroadway.

In the tire-making, the NW could be short or long, depending on theapplication need. The short NW is made at a temperature around 150-160°C. within a few hours. The long NW is made at a temperature above 160°C. and with a reaction time longer than 1 day.

Example 10

The TiO₂-containing, macro-sized nanofibers according to the presentinvention is also usable in making a multi-functional vest/coat fornanomedicine, battlefield, sports, space, firefighter, and the likes. Amulti-functional vest/coat 1300 is made at least partially with theTiO₂-containing, macro-sized nanofiber fabric. For example, as shown inFIG. 11, the multi-functional vest/coat 1300 has a plurality of areas1330 in a front and back panel 1310 and 1320 of the vest/coat 1300,which is made of the TiO₂-containing, macro-sized nanofiber fabric. Eachof the plurality of areas includes one or more of a minimum-invasionnanodrug delivery MEMS 1332, heating-releasing cartridge of nanodrugs1334, electrochemical nanobiosensor 1336, and the likes. Theseminimum-invasion nanodrug delivery MEMS 1332, heating-releasingcartridge of nanodrugs 1334, and electrochemical nanobiosensor 1336 arecontrollable, individually or in combination.

The foregoing description of the exemplary embodiments of the inventionhas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations are possiblein light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toenable others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the foregoing description and the exemplary embodiments describedtherein.

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1. A method of photocatalytically decomposing organic pollutants,comprising the steps of: (a) mixing a solution containing organicpollutants and a plurality of TiO₂-containing, macro-sizednanostructures to form a mixture, wherein the plurality ofTiO₂-containing, macro-sized nanostructures is provided in the form of amembrane or a sheet; (b) exposing the mixture to UV irradiation todecompose the organic pollutants; (c) soaking the membrane or sheet in avolume of an Mg(NO₃)₂ solution at room temperature (RT) for a firstperiod of time; (d) drying the membrane or sheet at RT; and (e) heatingthe dried membrane or sheet in air at a temperature in the range ofabout 25 to 300° C. for a second period of time.
 2. The method of claim1, wherein the UV irradiation is emitted from an irradiation source thatis positioned at a distance from the mixture.
 3. The method of claim 2,further comprising the steps of measuring the concentration of theorganic pollutants in the mixture before and after the exposing step. 4.The method of claim 3, wherein the decomposition of the organicpollutants is characterized with a ratio, R=(1−C_(t)/C₀), wherein C₀ andC_(t) are the measured concentration of the organic pollutants in themixture before and after the exposing step, respectively, and R is inthe range of from zero to one, and wherein when R=0, no organicpollutants in the mixture are decomposed, and when R=1, the organicpollutants in the mixture are completely decomposed after the exposingstep.
 5. The method of claim 3, wherein each measuring step is performedwith a UV-visible spectrometer.
 6. The method of claim 1, wherein thefirst period of time is in the range of about 0.1 to 15 hours, andwherein the second period of time is in the range of about 0.5 to 5hours.
 7. The method of claim 1, wherein the organic pollutants comprisea plurality of nerve agents (NA) or nerve agent simulants (NAS).
 8. Themethod of claim 7, wherein the nerve agent simulants (NAS) comprisediethyl phenylthiomethylphosphonate (DPTMP).
 9. The method of claim 1,wherein the UV irradiation has a wavelength, λ, in the range of about250 to 400 nm, and wherein the exposure time of the mixture to the UVirradiation is in the range of about 1-60 minutes.